Positive resist composition and method of formation of resist patterns

ABSTRACT

The invention provides a positive resist composition which has high etching resistance and attains high resolution, and a method of forming patterns by using the positive resist composition. The positive resist composition contains a resin component (A), which has acid dissociable, dissolution inhibiting groups, and exhibits increased alkali solubility under the action of acid, and an acid generator component (B) which generates acid on exposure, wherein the resin component (A) is a polymer comprising structural units (al) represented by the general formula (I) shown below, and a portion of the hydroxyl groups of the units (al) are protected by replacing the hydrogen atoms of the hydroxyl groups with acid dissociable, dissolution inhibiting groups represented by the general formula (II) shown below:  
                 
 
(wherein, R is a hydrogen atom or methyl group, R 1  is an alkyl group having 1 to 5 carbon atoms, R 2  is an alkyl group having 1 to 5 carbon atoms or a hydrogen atom, and X is an aliphatic polycyclic group having 10 to 16 carbon atoms or an aromatic polycyclic hydrocarbon group having 10 to 16 carbon atoms.)

TECHNICAL FIELD

The present invention relates to a positive resist composition and amethod of formation of resist patterns.

BACKGROUND ART

In recent years, advances in lithography techniques have lead toongoing, rapid miniaturization of resist patterns. Recently, levels ofresolution capable of forming line and space patterns of no more than100 nm, and isolated patterns of no more than 70 nm, are being demanded.

In the microprocessing technology used for realizing these highresolution levels, positive resist compositions that have been proposedas ideal resist materials, particularly for use in methods usingelectron beam exposure, typically employ a polyhydroxystyrene-basedresin, in which a portion of the hydroxyl groups have been protectedwith acid dissociable, dissolution inhibiting groups, as the base resin.

Examples of the most commonly used acid dissociable, dissolutioninhibiting groups include so-called acetal groups, including chain-likeether groups typified by 1-ethoxyethyl groups, and cyclic ether groupstypified by tetrahydropyranyl groups, as well as tertiary alkyl groupstypified by tert-butyl groups, and tertiary alkoxycarbonyl groupstypified by tert-butoxycarbonyl groups.

(Patent Reference 1)

Japanese Unexamined Patent Application, First Publication No.2002-341538

However, in microprocessing technology, the formation of high aspectratio, fine patterns, and particularly line and space patterns of nomore than 100 nm, has proven very difficult due to pattern collapsecaused by the surface tension of the developing solution. One possiblecountermeasure involves reducing the thickness of the resist film, butif the film thickness is reduced using conventional resist compositions,then the etching resistance tends to be inadequate.

DISCLOSURE OF INVENTION

The present invention takes the above problems associated with theconventional technology into consideration, with an object of providinga positive resist composition which exhibits a high level of etchingresistance and enables high resolution to be attained, as well as amethod of forming patterns that uses the positive resist composition.

As a result of intensive investigations aimed at achieving the aboveobject, the inventors of the present invention discovered that by usinga resin with bulky protective groups as the resin component used withinthe positive resist composition, the etching resistance could beimproved, enabling the thickness of the resist film to be reduced, andthey were hence able to achieve the above object and complete thepresent invention.

In other words, the present invention provides a positive resistcomposition that includes a resin component (A), which contains aciddissociable, dissolution inhibiting groups, and exhibits increasedalkali solubility under the action of acid, and an acid generatorcomponent (B) that generates acid on exposure, wherein the resincomponent (A) is a polymer containing structural units (a1) representedby a general formula (I) shown below, and a portion of the hydroxylgroups of the structural units (a1) are protected by substituting thehydrogen atoms of the hydroxyl groups with acid dissociable, dissolutioninhibiting groups represented by a general formula (II) shown below.

(wherein, R represents a hydrogen atom or a methyl group)

(wherein, R¹ represents an alkyl group of 1 to 5 carbon atoms, R²represents an alkyl group of 1 to 5 carbon atoms or a hydrogen atom, andX represents an aliphatic polycyclic group or an aromatic polycyclichydrocarbon group)

Furthermore, the present invention also provides a method of formingresist patterns that includes the steps of applying the above positiveresist composition to a substrate, conducting a prebake, performingselective exposure, and then conducting post exposure baking (PEB), andperforming alkali developing to form the resist pattern.

In this description, the term “structural unit” refers to a monomer unitthat contributes to the formation of a polymer.

Furthermore, the term “exposure” also includes irradiation with anelectron beam.

BEST MODE FOR CARRYING OUT THE INVENTION

As follows is a more detailed description of the present invention.

[Positive Photoresist Composition]

A positive resist composition of the present invention includes a resincomponent (A) (in this description also referred to as the component(A)”), which contains acid dissociable, dissolution inhibiting groups,and exhibits increased alkali solubility under the action of acid, andan acid generator component (B) (in this description also referred to asthe “component (B)”) that generates acid on exposure.

Regarding the component (A), the action of acid generated from theaforementioned component (B) by exposure causes the acid dissociable,dissolution inhibiting groups to dissociate, causing the entirecomponent (A) to change from an alkali insoluble state to an alkalisoluble state.

As a result, when a resist is exposed through a mask pattern during theformation of a resist pattern, or alternatively, is exposed and thensubjected to post exposure baking, the exposed portions of the resistshift to an alkali soluble state, whereas the unexposed portions remaininsoluble in alkali, meaning that alkali developing can then be used toform a positive resist pattern.

[Resin Component (A)]

The resin component (A) of a positive resist composition according tothe present invention contains the aforementioned structural units (a1)(in this description also referred to as “(a1) units”) as essentialstructural units, and a portion of the hydroxyl groups of these (a1)units are protected by substituting the hydrogen atoms of the hydroxylgroups with acid dissociable, dissolution inhibiting groups.

[(a1) Units]

The (a1) units are structural units represented by a general formula (I)shown below, and a portion of the hydroxyl groups of these (a1) unitsare protected by acid dissociable, dissolution inhibiting groupsrepresented by a general formula (II) shown below.

(wherein, R represents a hydrogen atom or a methyl group)

(wherein, R¹ represents an alkyl group of 1 to 5 carbon atoms, R²represents an alkyl group of 1 to 5 carbon atoms or a hydrogen atom, andX represents an aliphatic polycyclic group or an aromatic polycyclichydrocarbon group)

In the (a1) unit, R represents a hydrogen atom or a methyl group,although a hydrogen atom is preferred. If R is a hydrogen atom, then theprotection ratio for the hydroxyl groups can be improved, enabling thecontrast to be improved. Furthermore, the rate of dissolution followingdeveloping can also be improved. The bonding position of the hydroxylgroup may be the o-position, the m-position, or the p-position, althoughfrom the viewpoints of availability and cost, the p-position ispreferred.

A portion of the hydroxyl groups of the (a1) units must be protected byacid dissociable, dissolution inhibiting groups represented by the abovegeneral formula (II).

R¹ is a straight chain or branched alkyl group of 1 to 5 carbon atoms,and suitable examples include a methyl group, ethyl group, propyl group,isopropyl group, n-butyl group, isobutyl group, tert-butyl group, pentylgroup, isopentyl group, or neopentyl group. From an industrialviewpoint, a methyl group or ethyl group is preferred.

R² is an alkyl group of 1 to 5 carbon atoms or a hydrogen atom. Examplesof suitable alkyl groups of 1 to 5 carbon atoms include the samesubstituent groups described above for R¹. Of these, from an industrialviewpoint, R² is preferably a hydrogen atom.

X is an aliphatic polycyclic group or an aromatic polycyclic hydrocarbongroup, and is preferably an aliphatic polycyclic group of 10 to 16carbon atoms, or an aromatic polycyclic hydrocarbon group of 10 to 16carbon atoms. Of these groups, aliphatic polycyclic groups arepreferred, as they produce superior levels of line edge roughness, andrectangularity of the cross-sectional shape for the resulting resistpattern.

Examples of aliphatic polycyclic groups of 10 to 16 carbon atoms includegroups in which one hydrogen atom has been removed from a bicycloalkane,tricycloalkane or tetracycloalkane or the like. Specific examplesinclude groups in which one hydrogen atom has been removed from apolycycloalkane such as adamantane, norbornane, isobornane,tricyclodecane or tetracyclododecane. These types of polycyclic groupscan be appropriately selected from the multitude of groups proposed foruse with conventional ArF resists. Of these groups, adamantyl groups,norbornyl groups, and tetracyclododecanyl groups are preferredindustrially, and adamantyl groups are particularly desirable.

If X is an aliphatic polycyclic group, then a high level of resolutioncan be achieved, and the cross-sectional shape of the resist pattern isa favorable rectangular shape.

Examples of aromatic polycyclic hydrocarbon group of 10 to 16 carbonatoms include groups in which one hydrogen atom has been removed fromnaphthalene, anthracene, phenanthrene or pyrene. Specific examplesinclude a 1-naphthyl group, 2-naphthyl group, 1-anthracenyl group,2-anthracenyl group, 1-phenanthryl group, 2-phenanthryl group,3-phenanthryl group or 1-pyrenyl group, and of these, a 2-naphthyl groupis preferred industrially.

If X is an aromatic polycyclic hydrocarbon group, then the sensitivityis favorable, and the throughput is high, meaning the productivity canbe improved.

Specific examples of preferred forms of the acid dissociable,dissolution inhibiting group in an (a1) unit are shown below.

resist composition of the present invention, the polymer of thecomponent (A) may also be a copolymer that contains, in addition to theaforementioned (a1) units, the structural units (a2) (in thisdescription also referred to as “(a2) units”).[(a2) Units]

An (a2) unit is a structural unit represented by a general formula (III)shown below.

(wherein, R represents a hydrogen atom or a methyl group, R³ representsan alkyl group of 1 to 5 carbon atoms, and n represents either 0, or aninteger from 1 to 3)

R³ is a straight chain or branched alkyl group of 1 to 5 carbon atoms,and suitable examples include a methyl group, ethyl group, propyl group,isopropyl group, n-butyl group, isobutyl group, tert-butyl group, pentylgroup, isopentyl group, or neopentyl group. From an industrialviewpoint, a methyl group or ethyl group is preferred.

The aforementioned n is either 0, or an integer from 1 to 3. Of thesepossibilities, n is preferably either 0 or 1, and from an industrialviewpoint, is most preferably 0.

In those cases where n is from 1 to 3, the bonding position of thesubstituent group R³ may be the o-position, the m-position, or thep-position, and if n is 2 or 3, then any combination of substituentpositions is suitable.

In the present invention, the inclusion of (a2) units is not essential,but including them enables the alkali solubility to be controlled inaccordance with the (a2) unit content, and other benefits are alsoobtained, including a reduction in line edge roughness, and an abilityto produce favorable isolated line patterns. If (a2) units are used,then the quantity of such units is preferably within a range from 0.5 to25 mol %, and even more preferably from 3 to 20 mol %, relative to thecombined total of all the structural units that constitute the component(A). If the (a2) unit content is greater than this range, then line edgeroughness tends to increase, and favorable isolated lines become moredifficult to achieve.

In a positive resist composition of the present invention, as thecomponent (A), either a single polymer described above, or a mixture oftwo or more such polymers, may be used.

In those cases where a mixture of two or more polymers is used, any twoor more polymers selected from a group consisting of polymers containingthe aforementioned (a1) units, wherein a portion of the hydroxyl groupsof these (a1) units are protected by acid dissociable, dissolutioninhibiting groups, and copolymers containing the (a1) units and theaforementioned (a2) units, wherein a portion of the hydroxyl groups ofthe (a1) units are protected by acid dissociable, dissolution inhibitinggroups, can be used. In a preferred configuration, a mixture of apolymer containing the (a1) units, wherein a portion of the hydroxylgroups of these (a1) units are protected by acid dissociable,dissolution inhibiting groups, and a copolymer containing the (a1) unitsand the (a2) units, wherein a portion of the hydroxyl groups of the (a1)units are protected by acid dissociable, dissolution inhibiting groups,is used. By using this type of mixture as the component (A), the shapeof the formed resist pattern exhibits favorable rectangularity, and asuperior isolated line pattern can be obtained.

The weight average molecular weight (the polystyrene equivalent value,this also applies to all subsequent molecular weight values) of thepolymer of the component (A), prior to protection with the aciddissociable, dissolution inhibiting groups, is preferably within a rangefrom 2,000 to 30,000, and even more preferably from 5,000 to 20,000. Byensuring that the weight average molecular weight is no more than30,000, the solubility in the resist solvent can be improved, whereasensuring that the value is at least 2,000 enables a favorable resistpattern shape to be obtained.

Furthermore, in terms of the polydispersity (the weight averagemolecular weight divided by the number average molecular weight, thisalso applies below) of the polymer of the component (A), prior toprotection with the acid dissociable, dissolution inhibiting groups, amonodisperse component with a small polydispersity yields superiorresolution and is consequently preferred. Specifically, thepolydispersity is preferably no more than 2.0, and even more preferably1.5 or less.

In the present invention, the proportion of (a1) units that have beenprotected with acid dissociable, dissolution inhibiting groups, relativeto the combined total of all the structural units that constitute thepolymer of component (A), is preferably within a range from 5 to 35 mol%.

If the polymer contains no (a2) units, then the proportion of structuralunits that have been protected with acid dissociable, dissolutioninhibiting groups, relative to the combined total of all the structuralunits, is preferably within a range from 5 to 35 mol %, and even morepreferably from 20 to 30 mol %.

If the polymer contains (a2) units, then the proportion of structuralunits that have been protected with acid dissociable, dissolutioninhibiting groups, relative to the combined total of all the structuralunits, is preferably within a range from 5 to 35 mol %, and even morepreferably from 10 to 20 mol %.

By ensuring that the proportion is at least as large as the lower limitof the above range, favorable contrast can be achieved, whereas ensuringthat the proportion is no greater than the upper limit of the aboverange enables a developing defect suppression effect to be achieved.

The component (A) can be produced, for example, by polymerizing amonomer corresponding with (a1) in which the hydroxyl group is notprotected, and then using a known method to protect a portion of thehydroxyl groups of the (a1) units with acid dissociable, dissolutioninhibiting groups.

Furthermore, the component (A) can also be produced by preparing amonomer corresponding with (a1), in which the hydroxyl group has beenprotected with an acid dissociable, dissolution inhibiting group,subsequently polymerizing this monomer using normal methods, and thenusing hydrolysis to change a portion of the hydroxyl groups that havebeen protected with acid dissociable, dissolution inhibiting groups backto hydroxyl groups.

The quantity of the component (A) within a positive resist compositionof the present invention can be adjusted in accordance with the resistfilm thickness that is to be formed. Reported as a solid fractionconcentration, the quantity is typically within a range from 5 to 25% byweight, and even more preferably from 7 to 20% by weight.

[Acid Generator Component (B)]

In the present invention, as the acid generator component (B), acompound appropriately selected from known materials used as acidgenerators in conventional chemically amplified resists can be used.

Specific examples of suitable diazomethane-based acid generators includebis(isopropylsulfonyl)diazomethane, bis(p-toluenesulfonyl)diazomethane,bis(1,1-dimethylethylsulfonyl)diazomethane,bis(cyclohexylsulfonyl)diazomethane, andbis(2,4-dimethylphenylsulfonyl)diazomethane.

Specific examples of suitable onium salts include diphenyliodoniumtrifluoromethanesulfonate, (4-methoxyphenyl)phenyliodoniumtrifluoromethanesulfonate, bis(p-tert-butylphenyl)iodoniumtrifluoromethanesulfonate, triphenylsulfonium trifluoromethanesulfonate,(4-methoxyphenyl)diphenylsulfonium trifluoromethanesulfonate,(4-methylphenyl)diphenylsulfonium nonafluorobutanesulfonate,(p-tert-butylphenyl)diphenylsulfonium trifluoromethanesulfonate,diphenyliodonium nonafluorobutanesulfonate,bis(p-tert-butylphenyl)iodonium nonafluorobutanesulfonate, andtriphenylsulfonium nonafluorobutanesulfonate. Of these, onium saltscontaining a fluorinated alkylsulfonate ion as an anion are preferred.

Specific examples of suitable oxime sulfonate-based compounds includeα-(methylsulfonyloxyimino)-phenylacetonitrile,α-(methylsulfonyloxyimino)-p-methoxyphenylacetonitrile,α-(trifluoromethylsulfonyloxyimino)-phenylacetonitrile,α-(trifluoromethylsulfonyloxyimino)-p-methoxyphenylacetonitrile,α-(ethylsulfonyloxyimino)-p-methoxyphenylacetonitrile,α-(propylsulfonyloxyimino)-p-methylphenylacetonitrile, andα-(methylsulfonyloxyimino)-p-bromophenylacetonitrile. Of these,α-(methylsulfonyloxyimino)-p-methoxyphenylacetonitrile is preferred.

As the component (B), either a single acid generator or a combination oftwo or more different acid generators may be used.

The quantity used of the component (B) is typically within a range from1 to 20 parts by weight, and preferably from 2 to 10 parts by weight,per 100 parts by weight of the component (A). If the quantity is lowerthan the above range, then there is a danger that pattern formation maynot progress satisfactorily, whereas if the quantity exceeds the aboverange it becomes difficult to achieve a uniform solution, and there isalso a danger of a deterioration in the storage stability of thecomposition.

[Organic Solvent (C)]

A positive resist composition according to the present invention can beproduced by dissolving the materials in an organic solvent (C).

The organic solvent (C) may be any solvent capable of dissolving each ofthe components used to generate a uniform solution, and one or moresolvents selected from known materials used as the solvents forconventional chemically amplified resists can be used.

Specific examples of the organic solvent (C) include ketones such asacetone, methyl ethyl ketone, cyclohexanone, methyl isoamyl ketone and2-heptanone; polyhydric alcohols and derivatives thereof such asethylene glycol, ethylene glycol monoacetate, diethylene glycol,diethylene glycol monoacetate, propylene glycol, propylene glycolmonoacetate, dipropylene glycol, or the monomethyl ether, monoethylether, monopropyl ether, monobutyl ether or monophenyl ether ofdipropylene glycol monoacetate; cyclic ethers such as dioxane; andesters such as methyl lactate, ethyl lactate, methyl acetate, ethylacetate, butyl acetate, methyl pyruvate, ethyl pyruvate, methylmethoxypropionate, and ethyl ethoxypropionate. These organic solventscan be used alone, or as a mixed solvent of two or more differentsolvents.

There are no particular restrictions on the quantity used of the organicsolvent (C), which is selected to yield a concentration that is able tobe applied to a substrate or the like. The quantity of the organicsolvent (C) is selected so that the solid fraction concentration (thecombined total of the component (A), the component (B), the optionalcomponents (D) and (E) described below, and any other optionalcomponents) for the positive resist composition is within a range from 3to 30% by weight, and the actual quantity is set in accordance with thefilm thickness of the resist.

[Nitrogen-Containing Organic Compound (D)]

In a positive resist composition of the present invention, in order toimprove the resist pattern shape and the post exposure stability of thelatent image formed by the pattern-wise exposure of the resist layer, anitrogen-containing organic compound can also be added as a separate,optional component (D).

A multitude of these nitrogen-containing organic compounds have alreadybeen proposed, and any of these known compounds can be used, although asecondary aliphatic amine or tertiary aliphatic amine is preferred.Here, an aliphatic amine refers to an alkyl or alkylalcohol amine.

Specific examples of the component (D) include alkyl amines such astrimethylamine, diethylamine, triethylamine, di-n-propylamine,tri-n-propylamine, tripentylamine, tri-n-heptylamine, tri-n-octylamine,di-n-heptylamine, di-n-octylamine, and tri-n-dodecylamine; andalkylalcohol amines such as diethanolamine, triethanolamine,diisopropanolamine, triisopropanolamine, di-n-octanolamine, andtri-n-octanolamine. Of these, secondary or tertiary aliphatic aminescontaining an alkyl group of 7 to 15 carbon atoms are preferred. Byensuring that the component contains an alkyl group of 7 to 15 carbonatoms, the dispersion of the aliphatic amine through the resist patternis suppressed, enabling a more uniform distribution. In the presentinvention, alkyl amines such as tri-n-octylamine are particularlypreferred.

These compounds may be used alone, or in combinations of two or moredifferent compounds.

This component (D) is typically added in a quantity within a range from0.01 to 5.0 parts by weight per 100 parts by weight of the component(A).

Furthermore, in order to prevent any deterioration in sensitivity causedby the addition of the aforementioned component (D), and improve theresist pattern shape and the post exposure stability of the latent imageformed by the pattern-wise exposure of the resist layer, an organiccarboxylic acid, or a phosphorus oxo acid or derivative thereof can alsobe added as another optional component (E). The component (D) and thecomponent (E) can be used in combination, or either one can also be usedalone.

Examples of suitable organic caroxylic acids include malonic acid,citric acid, malic acid, succinic acid, benzoic acid, and salicylicacid.

Examples of suitable phosphorus oxo acids or derivatives thereof includephosphoric acid or derivatives thereof such as esters, includingphosphoric acid, di-n-butyl phosphate and diphenyl phosphate; phosphonicacid or derivatives thereof such as esters, including phosphonic acid,dimethyl phosphonate, di-n-butyl phosphonate, phenylphosphonic acid,diphenyl phosphonate, and dibenzyl phosphonate; and phosphinic acid orderivatives thereof such as esters, including phosphinic acid andphenylphosphinic acid, and of these, phosphonic acid is particularlypreferred.

The component (E) is typically used in a quantity within a range from0.01 to 5.0 parts by weight per 100 parts by weight of the component(A).

[Other Optional Components]

Other miscible additives can also be added to a positive resistcomposition of the present invention according to need, and examplesinclude additive resins for improving the properties of the resist film,surfactants for improving the ease of application, dissolutioninhibitors, plasticizers, stabilizers, colorants, and halationprevention agents.

The acid dissociable, dissolution inhibiting groups of the structuralunits (a1) introduced into the resin component (A) represent animportant characteristic of a positive resist composition of the presentinvention. Namely, by using the type of bulky acid dissociable,dissolution inhibiting groups described above, the etching resistancecan be improved, the thickness of the resist film can be reduced, andpattern collapse of the resist pattern can be prevented.

[Method of Forming Resist Patterns]

A method of forming a resist pattern according to the present inventioncan be conducted, for example, in the manner described below.

Namely, a positive resist composition described above is first appliedto the surface of a substrate such as a silicon wafer using a spinner orthe like, a prebake is conducted under temperature conditions of 80 to150° C. for 40 to 120 seconds, and preferably for 60 to 90 seconds, andthe resulting film is then subjected to selective exposure through adesired mask pattern with either an electron beam, or some other form ofradiation such as far ultraviolet radiation, using an electron beamexposure apparatus or the like. In other words, following exposurethrough a mask pattern, or direct patterning of the resist film with anelectron beam without using a mask pattern, PEB (post exposure baking)is conducted under temperature conditions of 80 to 150° C. for 40 to 120seconds, and preferably for 60 to 90 seconds. Subsequently, developingis conducted using an alkali developing solution such as a 0.1 to 10% byweight aqueous solution of tetramethylammonium hydroxide. In thismanner, a resist pattern that is faithful to the mask pattern can beobtained.

An organic or inorganic anti-reflective film may also be providedbetween the substrate and the applied layer of the resist composition.

There are no particular restrictions on the wavelength of the electronbeam or far ultraviolet radiation used for the exposure, and an ArFexcimer laser, KrF excimer laser, F₂ excimer laser, or other radiationsuch as EUV (extreme ultraviolet), VUV (vacuum ultraviolet), EB(electron beam), X-ray or soft X-ray radiation can be used.

A photoresist composition according to the present invention exhibitssuperior etching resistance to conventional compositions, enablesreductions in the thickness of the resist film, and prevents patterncollapse. Accordingly, because the composition is ideally suited formicroprocessing applications, it is particularly effective for use withan EB (electron beam).

Subsequently, the resist pattern obtained in the manner described aboveis typically used as a mask for conducting etching, thereby selectivelyremoving those portions of the substrate or the like not covered by theresist. A resist composition of the present invention exhibits improveddry etching resistance, and is consequently ideal for this role.

As the dry etching method, conventional methods including chemicaletching such as down-flow etching or chemical dry etching; physicaletching such as sputter etching or ion beam etching; orchemical-physical etching such as RIE (reactive ion etching) can beused.

The most typical type of dry etching is parallel plate RIE. In thismethod, first, a resist laminate is placed inside the RIE apparatuschamber, and the required etching gas is introduced. A high frequencyvoltage is then applied within the chamber, between an upper electrodeand the resist laminate holder which is positioned parallel to theelectrode, and this causes the generation of a gas plasma. The plasmacontains charged particles such as positive and negative ions andelectrons, as well as electrically neutral active seeds. As theseetching seeds adsorb to the lower resist layer, a chemical reactionoccurs, and the resulting reaction product breaks away from the surfaceand is discharged externally, causing the etching to proceed.

EXAMPLES

As follows is a description of examples of the present invention,although the scope of the present invention is in no way limited bythese examples. In evaluating the etching resistance, the etchingresistance observed for the comparative example 1 was used as thestandard by which the examples 1 to 10 were evaluated.

Example 1

First, the component (A) was prepared. Namely, poly(p-hydroxystyrene)(weight average molecular weight (Mw): 8,000, polydispersity (Mw/Mn):1.2) and adamantoxy vinyl ether were reacted together by normal methodsin the presence of an acid catalyst, thus forming a resin (A1) in whicha portion of the hydroxyl groups of the poly(p-hydroxystyrene) had beenprotected with acid dissociable, dissolution inhibiting groupsrepresented by the aforementioned formula (II-a).

When this resin was analyzed by ¹H-NMR, the quantity of aciddissociable, dissolution inhibiting groups represented by the formula(II-a) relative to the total number of hydroxyl groups fromp-hydroxystyrene was 26%. This indicates a protection ratio for thehydroxyl groups of 26 mol %.

Using this resin (A1) as the component (A), 100 parts by weight of thiscomponent (A), 6.0 parts by weight of triphenylsulfoniumtrifluoromethanesulfonate as the component (B), 0.675 parts by weight oftrioctylamine as the component (D), 0.27 parts by weight of salicylicacid, and 0.05 parts by weight of a non-ionic fluorine-silicone basedsurfactant (brand name: MEGAFAC R-08 (manufactured by Dainippon Ink andChemicals, Incorporated)) were dissolved in 1300 parts by weight ofpropylene glycol monomethyl ether acetate (hereafter abbreviated as“PM”), thus yielding a positive resist composition.

Meanwhile, a substrate was prepared by treating an 8 inch diametersilicon wafer with hexamethyldisilazane.

The positive resist composition obtained above was applied to thesurface of this substrate using a spinner, and then prebaked and driedon a hotplate at 110° C. for 90 seconds, forming a resist layer with afilm thickness of 200 nm.

Next, this photoresist layer was exposed using an electron beamlithography apparatus (HL-800D, manufactured by Hitachi, Ltd.,accelerating voltage 70 kV), using a method in which the pattern wasformed by direct irradiation of the electron beam onto the photoresistlayer.

A PEB treatment was then performed at 110° C. for 90 seconds, and thephotoresist layer was subjected to puddle development for 60 seconds at23° C. in a 2.38% by weight aqueous solution of tetramethylammoniumhydroxide, and then rinsed with pure water for 30 seconds. The resistwas then shaken dry, and then further dried by heating at 100° C. for 60seconds, thus forming a 1:1 line and space resist pattern.

Inspection of the thus obtained resist pattern using a SEM (scanningelectron microscope) confirmed that excellent resolution could beobtained at a line width of 80 nm. Furthermore, the cross-sectionalshape of the resist pattern was rectangular. Moreover, no patterncollapse had occurred.

Subsequently, using the thus obtained resist pattern as a mask, anetching rate test was conducted by subjecting the substrate to dryetching. Namely, when the etching rate was measured using a mixed gas ofoxygen and tetrafluoromethane as the etching gas, the etching rate was1.3 times slower than the rate observed in the comparative example 1,indicating an excellent level of etching resistance.

Example 2

With the exception of altering the component (B) toα-(methylsulfonyloxyimino)-p-methoxyphenylacetonitrile, testing wasconducted in use same manner as the example 1. Inspection of theobtained resist pattern using a SEM (scanning electron microscope)confirmed that excellent resolution could be obtained at a line width of80 nm. Furthermore, the cross-sectional shape of the resist pattern wasrectangular. Moreover, no pattern collapse had occurred. When theetching rate was measured, the etching rate was 1.3 times slower thanthe rate observed in the comparative example 1, indicating an excellentlevel of etching resistance.

Comparative Example 1

A resin component containing poly(p-hydroxystyrene) (weight averagemolecular weight (Mw): 8,000, polydispersity (Mw/Mn): 1.2) in which aportion of the hydroxyl groups had been protected with 1-ethoxyethylgroups (hydroxyl group protection ratio: 45 mol %) was used instead ofthe resin (A1) of the component (A) from the example 1. With theexception of using this resin component, a resist composition wasprepared in the same manner as the example 1.

Following formation of a 90 nm 1:1 line and space pattern using thisresist composition, in the same manner as the example 1, an etching ratetest was conducted. The results of this test revealed that the etchingresistance was inferior to that observed for the examples 1 through 10.Furthermore, some slight pattern collapse was also observed.

Example 3

First, the component (A) was prepared. Namely, poly(p-hydroxystyrene)(weight average molecular weight (Mw): 8,000, polydispersity (Mw/Mn):1.2) and naphthoxy vinyl ether were reacted together by normal methodsin the presence of an acid catalyst, thus forming a resin (A2) in whicha portion of the hydroxyl groups of the poly(p-hydroxystyrene) had beenprotected with acid dissociable, dissolution inhibiting groupsrepresented by the aforementioned formula (II-b).

When this resin was analyzed by ¹H-NMR, the quantity of aciddissociable, dissolution inhibiting groups represented by the formula(II-b) relative to the total number of hydroxyl groups fromp-hydroxystyrene was 26%. This indicates a protection ratio for thehydroxyl groups of 26 mol %.

With the exception of using this resin (A2) as the component (A), apositive resist composition was prepared in the same manner as theexample 1.

Using the thus obtained positive resist composition, a 1:1 line andspace pattern was formed in the same manner as the example 1.

Inspection of the thus obtained resist pattern confirmed that excellentresolution could be obtained at a line width of 80 nm. Furthermore,although the cross-sectional shape of the resist pattern was slightlytapered, no pattern collapse had occurred. When the etching rate wasmeasured, the etching rate was 1.1 times slower than the rate observedin the comparative example 1.

In these examples, the term “slightly tapered” means the shape is veryclose to rectangular, with just a hint of tapering.

Example 4

With the exception of altering the component (B) toα-(methylsulfonyloxyimino)-p-methoxyphenylacetonitrile, testing wasconducted in the same manner as the example 3. Inspection of theobtained resist pattern using a SEM (scanning electron microscope)confirmed that excellent resolution could be obtained at a line width of80 nm. Furthermore, although the cross-sectional shape of the resistpattern was slightly tapered, no pattern collapse had occurred. When theetching rate was measured, the etching rate was 1.1 times slower thanthe rate observed in the comparative example 1.

Example 5

First, the component (A) was prepared. Namely, a copolymer ofp-hydroxystyrene and styrene (molar ratio: 85:15, weight averagemolecular weight (Mw): 8,000, polydispersity (Mw/Mn): 1.2) andadamantoxy vinyl ether were reacted together by normal methods in thepresence of an acid catalyst, thus forming a resin (A3) in which aportion of the hydroxyl groups of the p-hydroxystyrene structural unitscontained within the copolymer had been protected with acid dissociable,dissolution inhibiting groups represented by the aforementioned formula(II-a).

When this resin was analyzed by ¹H-NMR, the ratio of the total number ofhydroxyl groups from p-hydroxystyrene relative to the number of aciddissociable, dissolution inhibiting groups represented by the formula(II-a) was 70:15. This indicates that the proportion of structural unitsprotected by the acid dissociable, dissolution inhibiting groupsrelative to the total number of structural units contained within theresin (A3) was 15 mol %.

With the exception of using this resin (A3) as the component (A), apositive resist composition was prepared in the same manner as theexample 1.

Using the thus obtained positive resist composition, a 1:1 line andspace pattern was formed in the same manner as the example 1.

Inspection of the thus obtained resist pattern confirmed that excellentresolution could be obtained at a line width of 120 nm. Furthermore,although the cross-sectional shape of the resist pattern was slightlytapered, no pattern collapse had occurred. When the etching rate wasmeasured, the etching rate was 1.4 times slower than the rate observedin the comparative example 1, indicating an excellent level of etchingresistance.

Example 6

With the exception of altering the component (B) toα-(methylsulfonyloxyimino)-p-methoxyphenylacetonitrile, testing wasconducted in the same manner as the example 5. Inspection of theobtained resist pattern confirmed that excellent resolution could beobtained at a line width of 120 nm. Furthermore, although thecross-sectional shape of the resist pattern was slightly tapered, nopattern collapse had occurred. When the etching rate was measured, theetching rate was 1.4 times slower than the rate observed in thecomparative example 1, indicating an excellent level of etchingresistance.

Example 7

With the exception of using a mixed resin of the resin (A1) obtained inthe example 1 and the resin (A3) obtained in the example 3 (molar ratio20:80) as the component (A), a positive resist composition was preparedin the same manner as the example 1.

Using the thus obtained positive resist composition, a 1:1 line andspace pattern was formed in the same manner as the example 1.

Inspection of the thus obtained resist pattern confirmed that excellentresolution could be obtained at a line width of 80 nm. Furthermore, thecross-sectional shape of the resist pattern was rectangular, and nopattern collapse had occurred. When the etching rate was measured, theetching rate was 1.4 times slower than the rate observed in thecomparative example 1, indicating an excellent level of etchingresistance.

Example 8

With the exception of altering the component (B) toα-(methylsulfonyloxyimino)-p-methoxyphenylacetonitrile, testing wasconducted in the same manner as the example 7. Inspection of theobtained resist pattern using a SEM (scanning electron microscope)confirmed that excellent resolution could be obtained at a line width of80 nm. Furthermore, the cross-sectional shape of the resist pattern wasrectangular, and no pattern collapse had occurred. When the etching ratewas measured, the etching rate was 1.4 times slower than the rateobserved in the comparative example 1, indicating an excellent level ofetching resistance.

Example 9

With the exception of using a mixed resin of the resin (A2) obtained inthe example 2 and the resin (A3) obtained in the example 3 (molar ratio50:50) as the component (A), a positive resist composition was preparedin the same manner as the example 1.

Using the thus obtained positive resist composition, a 1:1 line andspace pattern was formed in the same manner as the example 1.

Inspection of the thus obtained resist pattern confirmed that excellentresolution could be obtained at a line width of 120 nm. Furthermore,although the cross-sectional shape of the resist pattern was slightlytapered, no pattern collapse had occurred. When the etching rate wasmeasured, the etching rate was 1.2 times slower than the rate observedin the comparative example 1, indicating an excellent level of etchingresistance.

Example 10

With the exception of altering the component (B) toα-(methylsulfonyloxyimino)-p-methoxyphenylacetonitrile, testing wasconducted in the same manner as the example 9. Inspection of theobtained resist pattern confirmed that excellent resolution could beobtained at a line width of 120 nm. Furthermore, although thecross-sectional shape of the resist pattern was slightly tapered, nopattern collapse had occurred. When the etching rate was measured, theetching rate was 1.4 times slower than the rate observed in thecomparative example 1, indicating an excellent level of etchingresistance.

EFFECTS OF THE INVENTION

As described above, according to the present invention there areprovided a positive resist composition which exhibits a high level ofetching resistance and enables high resolution to be attained, and amethod of forming patterns that uses the positive resist composition.

1. A positive resist composition, comprising a resin component (A) whichcontains acid dissociable, dissolution inhibiting groups, and exhibitsincreased alkali solubility under action of acid, and an acid generatorcomponent (B) that generates acid on exposure, wherein said resincomponent (A) is a polymer comprising structural units (a1) representedby a general formula (I) shown below, and a portion of hydroxyl groupsof said structural units (a1) are protected by substituting hydrogenatoms of said hydroxyl groups with acid dissociable, dissolutioninhibiting groups represented by a general formula (II) shown below:

(wherein, R represents a hydrogen atom or a methyl group)

(wherein, R¹ represents an alkyl group of 1 to 5 carbon atoms, R²represents an alkyl group of 1 to 5 carbon atoms or a hydrogen atom, andX represents an aliphatic polycyclic group or an aromatic polycyclichydrocarbon group).
 2. A positive resist composition according to claim1, wherein said polymer of said component (A) further comprisesstructural units (a2) represented by a general formula (III) shownbelow:

(wherein, R represents a hydrogen atom or a methyl group, R³ representsan alkyl group of 1 to 5 carbon atoms, and n represents either 0, or aninteger from 1 to 3).
 3. A positive resist composition according toclaim 2, wherein said component (A) is a mixture of a polymer, whichcomprises said structural units (a1), and in which a portion of hydroxylgroups of said structural units (a1) are protected with said aciddissociable, dissolution inhibiting groups, and a copolymer, whichcomprises said structural units (a1) and said structural units (a2), andin which a portion of hydroxyl groups of said structural units (a1) areprotected with said acid dissociable, dissolution inhibiting groups. 4.A positive resist composition according to claim 1, wherein said group Xis an adamantyl group or a naphthyl group.
 5. A positive resistcomposition according to claim 1, wherein said group R is a hydrogenatom.
 6. A positive resist composition according to claim 1, wherein aweight average molecular weight of said polymer of said component (A),prior to protection with said acid dissociable, dissolution inhibitinggroups, is within a range from 2,000 to 30,000.
 7. A positive resistcomposition according to claim 1, wherein a polydispersity of saidpolymer of said component (A), prior to protection with said aciddissociable, dissolution inhibiting groups, is no more than 2.0.
 8. Apositive resist composition according to claim 1, wherein a proportionof said structural units (a1) that have been protected with said aciddissociable, dissolution inhibiting groups, relative to a combined totalof all structural units that constitute said polymer of said component(A), is within a range from 5 to 35 mol %.
 9. A positive resistcomposition according to claim 1, further comprising anitrogen-containing organic compound (D), wherein said component (D)comprises a secondary or tertiary aliphatic amine containing an alkylgroup of 7 to 15 carbon atoms.
 10. A positive resist compositionaccording to claim 1, which can be used in a method of forming resistpatterns comprising an exposure step that uses an electron beam.
 11. Amethod of forming resist patterns, comprising steps of applying apositive resist composition according to claim 1 to a substrate,conducting a prebake, performing selective exposure, and then conductingpost exposure baking (PEB), and performing alkali developing to form aresist pattern.